Quote from: BlackHatCoiner on Today at 01:13:31 PM

In this case, shouldn't the CoinJoin/Lightning software warn for unconfirmed parent(s)? I wouldn't accept a non-RBF transaction which has an unconfirmed RBF-enabled parent as "settled".

The UTXO used in the coinjoin transaction doesn't have any unconfirmed parent at all.
That UTXO was combined with another UTXO in a different transaction at the same time as the coinjoin transaction. This is the transaction which was invalided with doubling-spending its parent.
As both transactions have been made at the same time, it's possible that the client see the coinjoin transaction before the other one and doesn't understand what's causing the issue.
This is my understanding from o_e_l_e_o's post and I really don't know how likely this is.

Quote from: BlackHatCoiner on Today at 01:13:31 PM

I wouldn't accept a non-RBF transaction which has an unconfirmed RBF-enabled parent as "settled".

Me too.

Quote from: BlackHatCoiner on Today at 01:13:31 PM

You mean can't be propagated and confirmed?

No. The "Can" is true.